MODULE 3
SEA PLANTS
Key Concepts:
1. Explain why Sea Plants are an important component of aquatic ecosystems (and
the planet, as a whole).
2. Name the colour groupings (and division classification) of aquatic algae ( you need
not remember the specific chemicals and pigments that cause these).
3. Identify the important, commercially useful chemicals that each colour group of
algae produce.
4. Be able to identify plants commonly found at the Touch Pool (indicated in the notes
by means of **) from samples and pictures.
5. Explain the distinguishing features of all plants mentioned in point 4.
6. Highlight any special or exceptional structural adaptations exhibited by the plants
mentioned in point 4.
7. Explain any specific uses of these plants.
8. Identify any commercially useful chemicals extracted from these plants and...
9. Explain general uses of these chemicals (eg food colouring) and specific products
resulting from that (eg. Margarine, yellow cheese etc).
10. Explain the structure of a Kelp forest and the Ecology, in terms of food webs and
energy flow.
1. SEA PLANTS (ALGAE) AND THEIR BIOLOGY
INTRODUCTION
The term algae is a general name that can be given to
‘seaweeds’ or sea plants, as they should more correctly be
called. Sea plants are simple marine plants that grow in the
shallow waters at the edge of the world's oceans. Together
with microscopic algae called phytoplankton, sea plants
contribute to the food chain in the sea, provide homes for
many different sea animals, lend beauty to the underwater
landscape, and are directly valuable to man as food and as
industrial raw material.
Algae make their own food (primary producers)
Sea plants use solar energy to produce carbohydrate food
from carbon dioxide and water through the process of
photosynthesis. During this process, oxygen is given off as a
by-product.
Algae are considered simple ‘plants’
Sea plants are simpler than most land plants because they
have no roots or shoots. Sea plants absorb their nutrients
directly from the surrounding seawater; they therefore have
no need for roots or complex conductive tissue. Some large
sea plants like the kelps do, however, have root-like
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attachment structures called holdfasts, stem like stipes and leaf-like fronds.
Algae can be grouped based on their colour
Sea plants can be divided into three groups: green, brown and red. They are so grouped according
to the photosynthetic and accessory pigments that they possess which in turn will reflect certain
colours of light producing what appear to be green, brown and red sea plants. All sea plants
contain chlorophyll a – the photosynthetic pigment.
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Green Algae: Like land plants, green algae contains chlorophyll a & b, which they use to
capture light energy during photosynthesis. These chlorophyll pigments reflect green light
making them appear green in colour.
Brown Algae: Brown algae are usually yellowish-brown with grey or blackish tinges. This is
so because of the presence of chlorophyll a and c plus an additional accessory xanthophyll
pigment called fucoxanthin from which brown sea plants derive their colour. Some brown
sea plants however are often totally black in colour and are often mistaken for red sea
plants that are dark in colour.
Red Algae: Red algae possess only the chlorophyll a – the principal photosynthetic pigment.
They appear red because they possess a series of accessory pigments known as phycobilins
that absorb blue and green light and reflect red light. Although they are commonly called
red sea plants, some may appear black, blue, yellow and even green. This is especially true
for intertidal red sea plants whose red pigments may become masked by the chlorophyll
and other pigments present in them. Since blue light penetrates water to a greater depth
than any other light, the phycobilins present in red sea plants allow these sea plants to
photosynthesise and survive at great depths; some red sea plants are known to occur to
depths of up to 250 meters!
2. GREEN ALGAE (DIVISION CHLOROPHYTA)
Green algae are thought to be ancestors of land plants because they possess the same green
pigments (chlorophyll a & b). Below are the common green sea plants of the
Cape Peninsula.
**Sea lettuce (Ulva sp)
Ulva species are called sea lettuce. These green sea plants may form dense
clumps of membranous blades, only two cells thick that resemble lettuce
leaves. It is regarded as edible and used extensively in oriental cooking.
**Green sea intestines (Enteromorpha intestinalis)
This is aptly named the green sea intestines because the sea plant is made up of
membranous green tubes (often collapsed) only one cell thick, resembling an
intestine.
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Two Oceans Aquarium Volunteer Training Manual – Module 3 - INTRO TO SEA PLANTS
Sea lettuce and green sea intestines are fast growing opportunistic sea plants that have a wide salt
and temperature tolerance. These features enable them to rapidly colonise any part of the rocky
seashore if the conditions are right. They are often very abundant high up the shore where
desiccation stress is the primary factor controlling sea plant distribution. Under sheltered
conditions, these sea plants may be the only sea plants to occupy entire high shore tide pools with
sea lettuce plants often attaining lengths in excess of half a meter. When areas of the seashore
become disturbed, these are the sea plants that would be the first to appear because of their
ability to rapidly colonize free space.
**Upright codium (Codium fragile)
Upright codium is a forked, upright, somewhat velvety, spongy sea plant
that is able to regulate the movement of its chloroplasts to maximize
photosynthesis. This sea plant’s thallus is internally composed of
interlocking filaments that end in club-like structures bearing the
chloroplasts and the reproductive structures. Codium fragile belongs to a
group of sea plants that are unique in that their internal filaments lack
cross-walls. Thus, instead of being divided into cells, each filament is a
giant cell with many nuclei. Codium fragile is particularly abundant in
intertidal rockpools that are also prone to sand inundation.
**Strap caulerpa (Caulerpa filiformis)
Strap caulerpa grows as a tangled mass of root-like rhizomes giving rise to
cylindrical stipes bearing bright grass green, flattened blades. The blades that are
often mottled with dark-green spots are once or twice dichotomously (into two)
branched. Like the Codiums, this sea plants internal structure is composed of
multinucleated filaments, lacking cross-walls and thus essentially lacking a cellular
structure. Despite this, strap caulerpa is amazingly tough and has a complex
morphology. This sea plant maintains its form due to the presence of a complex
mesh of cellulose ribs formed within an otherwise hollow structure. Also, like the
Codiums, the lack of cross-walls allows this sea plant to regulate the movements of
its chloroplasts, maximizing its photosynthetic capacity. It is not surprising that sea
plants such as these are quite frequently found dominating areas prone to sand
inundation.
USES OF ALGAE
Together with microscopic algae called phytoplankton, sea plants form the basis of the food chain
in the sea and are directly valuable to humans. Although we can neither smell nor taste them,
many ingredients in our foods and household products come from the sea and from sea plants.
GREEN ALGAE
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Sea lettuce (Ulva species) as a whole plant has long been eaten in the Far East as a green
vegetable in salads and soups.
Beta-carotene, a natural pigment derived from green sea plants, is used as a yellow-orange
food colorant in cheese, coffee creamers, egg substitute, margarine, mayonnaise,
multivitamins, salad dressing, and many more.
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Commercial use of algae in South Africa.
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At present a small industry utilising mostly brown and fleshy red sea plants. The increasing
use of local representatives of sea plants has now resulted in a state policy to ensure the
sustainable use of these commercial resources. This awareness has greatly increased
research on local sea plants and considerably increased our knowledge of most of the
species. It is only with this increased awareness that we have been able to bring to you the
knowledge that we have gained regarding this fascinating group of marine organisms. Now
that you’ve come to know the green, brown and red sea plants in a bit more detail, we hope
that you will see them with a positive view and not just that smelly stuff lying on the beach.
QUICK REVIEW
1. What colour groups of marine algae do we find, and explain (without going into detail of
chemical names) why they exhibit these colours.
2. Are marine algae only found near to the coastline? Explain.
3. What are some general uses of sea plants?
4. Where are Sea lettuce and Sea intestines likely to be found?
5. Where are Upright codium and Strap caulerpa likely to be found? What structural
feature makes this possible?
6. What chemical is extracted from plants like Sea lettuce, and what are some of its uses
and applications?
3. BROWN ALGAE (DIVISION PHAEOPHYTA)
Unlike the green sea plants, brown sea plants are generally slower growing and
are less tolerant of salinity and temperature extremes and thus more prone to
desiccation stress. They therefore tend to occur lower down on the shore than
the green sea plants. Below are the common brown sea plants of the Cape
Peninsula.
Cape cord-weed (Chordariopsis capensis)
Chordariopsis capensis, is a stringy, limp sea plant often abundant in sheltered
high shore and mid-shore tide pools. Here it occurs in a flaccid
untidy mass that easily becomes dislodged by any significant
amount of wave action.
**Dead-man’s fingers (Splachnidium rugosum)
Spachnidium rugosum, aptly called the dead-man's fingers, has spotted; elongated,
cylindrical branches that resemble withered and callused fingers. The branches,
sometimes also berry-like are filled with clear viscous mucous. It is this mucus that
enables the plant to withstand a high degree of desiccation stress within the midintertidal when it becomes exposed at low tide.
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Ralfsia (Ralfsia verrucosa)
Ralfsia verrucosa, is an olive brown to khaki encrusting brown sea plant
that occurs abundantly in low shore tide pools. Here it often forms large,
flat, smooth expanses giving the impression that someone had
accidentally dropped khaki paint into the tide pools. Ralfisia can occur in
high abundance because of its relatively fast growth rate and also because
it produces a chemical which seems to deter most grazers. However the
periwinkle and the long-spined limpet like to eat Ralfsia, and
the latter even ‘gardens’ this brown sea plant.
**Hanging wrack (Bifurcaria brassicaeformis)
The hanging wrack commonly dominates that part of the low shore just above the
subtidal zone where it forms extensive mats of long, tough, cylindrical branches looking
very much like an unmown lawn. This sea plant achieves dominance of the low shore by
rhizomatous spreading of its holdfast. Some local scientists have recorded individual
sea plant bases measuring as much as 1m in diameter. This species is endemic to South
Africa, having a very restricted distribution; it occurs only from Cape Agulhas to around
Sea Point in Cape Town.
Long-leafed sargassum (Anthophycus longifolius) -Mainly in displays.
The long-leafed sargassum is a somewhat twisted, robust and knobbled sea plant that
can easily dominate large areas of low shore tide pools and the immediate subtidal.
The blades of this species are characteristically toothy with those blades near the
surface bearing little bladders in their axils. These bladders keep the sea plant afloat
enabling it to maximise its photosynthetic abilities. Long-leafed sargassum is one of
the largest non-kelp brown sea plants, often attaining lengths in excess of 1m. This sea
plant is the sole species in the genus Anthophycus and this genus is known only from
Southern Africa. This species is therefore endemic to South Africa.
KELP
In the subtidal and intertidal gullies of the southwest Cape, the west coast and east coast, we can
see the giant brown sea plants known as kelp. Like trees in an ancient forest, kelps dominate the
canopy of the subtidal zone in the cool, nutrient-rich waters of South African. The word ‘kelp’
originally referred to the ash of these plants, which was used as a fertilizer in Europe. Kelp is the
largest and fastest growing of the sea plants, growing as much as 13 mm in a day. Some of these
sea plants such as the giant kelp (Macrocystis pyrifera) of central and southern California are
known to grow to over 30 m in length, growing at the incredible rate of up to 50 cm per day.
Unlike most sea plants that are relatively simple in structure, kelp plants have reached a level of
specialization near to that of the higher green plants. Because they are so large, these brown sea
plants have developed specialized tissues and organs. Such specialized tissues include conductive
tissue for transporting the products of photosynthesis internally; yet others include reproductive,
photosynthetic, and strengthening tissue. Specialized organs include an elaborate root-like
holdfast purely for attachment, a stem-like stipe that bears the photosynthetic and reproductive
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blades, and many possess floats that keep the sea plant and its blades erect in the water column.
All these features have improved the kelps photosynthetic ability, allowing them to form extensive
beds, dominating the subtidal zone.
Below are the common kelp species of the Cape Peninsula.
**Sea bamboo (Ecklonia maxima)
Ecklonia maxima, is the largest of the local kelp species, dominating the
inshore regions of the southern and west coast. This sea plant possesses a
massive holdfast that extends into a long, hollow, gas-filled stipe up to 15 m in
length that ends in a bulb (float) at its apex. The bulb further extends into a
flat, solid primary blade from which secondary blades emerge. These
secondary blades can reach 3 m in length. Because of its hollow stipe and bulb,
this species is buoyant, its blades frequently breaking the surface of the ocean
at low tide. So, when you see kelp at the ocean’s surface, this is most often sea
bamboo. This also means that sea bamboo constitutes the canopy of the kelp
forest and it is here that three species of red sea plant and a limpet occur
epiphytically on the sea bamboo. While this species is the dominant kelp in
inshore waters of the southern and west coast, it becomes progressively
replaced by another kelp species, the split-fan kelp, in deeper waters and also
further north up the west coast.
**Split-fan kelp (Laminaria pallida)
Laminaria pallida lacks the buoyant structures found in sea bamboo (although the
stipes of several plants have been shown to be hollow), so it rarely breaks the
surface in deeper water. This species grows to about 10 m in length and possesses
a single broad, fan-shaped blade that becomes irregularly split, giving the kelp its
name. Unlike sea bamboo, which is more common in relatively shallow water, splitfan kelp occurs to depths of 30 m. Adult split-fan kelp plants have warty stipes
whereas they are smooth in the sea bamboo. Both of these sea plants are common
on wave-exposed rocky shores.
**Bladder kelp (Macrocystis angustifolia)
The bladder kelp, (Macrocystis angustifolia) is the least common
of the west coast kelp species. This kelp is a relatively delicate, vine-like species
bearing numerous blades at regular intervals along its slender stipe. At its apex,
the new blades are fused, gradually separating as they grow. The blades possess
numerous marginal spines and a single gas-filled bladder at their bases. It is
these bladders that allow this kelp to remain afloat and erect in the water
column. Unlike the other two species of kelp, an individual rhizomatously
spreading holdfast in this species can bear multiple stipes. Large populations of
this sea plant are found only at two locations near Cape Town; one at
Kommetjie, the other at Robben Island in the Melkbostrand region. Unique to
this species of kelp are its haphazardly rippled blades. This feature is especially
important, as it allows for increased absorption of nutrients in relatively low flow
environments typical of sheltered lagoons or embayments.
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USES OF BROWN ALGAE
A characteristic feature of brown sea plants is that their cell walls are made of cellulose
strengthened by calcium alginate. Alginate is a substance of considerable economic importance as
it is used as a gelling and emulsifying agent in a number of industries. Surprisingly though, at
present, only kelp is harvested commercially in South Africa for alginate extraction. Perhaps it is
because no other group of brown sea plant occurs in large enough densities to be commercially
viable.
In South Africa, the sea plant industry is based on sea bamboo and split-fan kelp, but includes
some other brown and red sea plants.
USES OF KELP
Internationally, a huge market exists for the harvesting of kelp and other brown sea plants for
alginate production.
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Fertilizer
Kelp is widely used as a fertilizer and is harvested extensively as feed for commercially
farmed abalone.
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Nutritional supplement.
Sea bamboo is also used as a nutritional supplement for farm animals. In local agriculture,
this kelp is well known for the production of a very successful plant growth stimulant. It is
also a great source of micronutrients.
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Food industry.
It makes water-based products thicker, creamier, and more stable over extreme differences
in temperature, pH, and time. For example, alginates prevent the formation of ice crystals in
ice cream. Other products containing alginate include brownie mix, frozen foods, desserts,
relishes, salad dressing, sauces, gravies and even beer.
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Cosmetics, pharmaceutical, paint, textile and welding industries.
Alginate aids in the suspension and stabilizing of agents over ranges of temperature and pH.
In the paper industry, for example, alginate is important as it enables sizing and polishing of
the finished paper product. Did you know that alginate from kelp is even used to make
fibres for high quality audio speakers?
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Medical industry.
Kelp is especially important as its alginate is used to encapsulate many things such as tablets
in powder form, fracture castings and moulds, and even organs for transplant.
Kelp also contains an astonishing amount of vitamins and minerals. The most important of
these supplements though is probably iodine. Iodine has a normalising effect on the thyroid
gland (this gland controls the body’s growth and development). In Namibia, scientists are
looking to use sea bamboo and split-fan kelp as a treatment of goitre and prevention of (or
reduction in the occurrence of) cretinism in southern Africa. Similarly, because iodine feeds
the thyroid, kelp is even used in weight loss formulas. Japanese studies have even shown a
direct relationship between alginate contained in kelp and the prevention of breast cancer.
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QUICK REVIEW
1. If you show Dead man’s fingers to a child at the touch pool, what two features can you
ask them to look at/ feel?
2. What does endemic mean?
3. Although they look superficially similar, how do Long leaf sargassum and Bladder kelp
differ structurally?
4. Why do many sea plants found in deeper water have bladders?
5. How do Sea bamboo and Split fan kelp differ?
6. How are rippled blades, as seen on bladder kelp, useful to them?
7. What chemical is commercially extracted from kelp?
8. Explain uses of kelp and the chemical mentioned above in the Farming sector, Food
industry, Medical field and Elsewhere...
4.
KELP FOREST STRUCTURE AND FOOD WEBS
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Ecologically, the kelp forest provides an important, complex, three-dimensional habitat for a
number of species of fish, invertebrates and other sea plants. The kelp limpet, Cymbula compressa
for example, occurs only on sea bamboo. Kelp beds are among the most productive ecosystems on
earth, supporting high primary production levels. This high productivity forms the base of many
coastal food webs in cool water environments worldwide. So, both directly and indirectly, they are
an important food source for a large variety of invertebrates, fish, mammals and seabirds.
Furthermore, kelp is tough and resilient, and stretching into the sea, often for many kilometres,
they help break the great force of the waves offering protection to the near-shore ecosystem.
4.1 KELP FOREST STRUCTURE
Canopy species: In the kelp beds typical of the southern-west coast, the blades form a canopy
layer near the surface. The canopy absorbs much of the light reaching the water surface, so most
of the stipes of mature plants is in a twilight zone.
Epiphytes: Like terrestrial creepers and ferns, marine epiphytes grow attached to the kelp blades
and portions of the stipes near the surface and so doing receive as much light as the blades.
Epiphytes are generally delicate in nature, as they have to bend as the kelp sways in the waves.
Under storey species: On the rock, underneath the kelp canopy occur numerous species of sea
plants that make up the under storey layer. These species live in a dim world, since the canopy and
the epiphytes intercept much of the incoming light. Nevertheless, there is enough light to support
a broad variety of under storey flora, many of which are able to photosynthesize even at very low
levels of light. Many of these under storey sea plants are flat, to capture as much light as possible.
4.2 FOOD WEBS IN THE KELP FOREST
The South African kelp ecosystem has been described as a sun-powered system, with additional
energy input in the form of wind and waves.
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Energy from sunlight drives primary production, as well as setting up a thermally stratified
water column.
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Wind energy drives the upwelling process, which brings nutrients up to the surface waters
in which the kelps grow. The uptake of nutrients is enhanced by water motion due to wave
action, and this allows the kelp and associated sea plant to make better use of the sunlight
for primary production.
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Energy from waves can also uproot kelp plants and wash them up onto the shore, where
they provide food for a wide variety of organisms, especially amphipod and isopod
crustaceans. Wave energy contributes to the erosion of the blades, producing particulate
and dissolved organic matter.
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Wave action keeps kelp plants in motion, and prevents grazers from climbing and damaging
the plants.
4.3 ENERGY FLOW
This is the movement of energy through the food web of an ecosystem, from sunlight to the
primary producers, and from primary producers to consumers and decomposers.
Kelp energy is not used only within the kelp bed it also helps to support other adjacent
ecosystems. Every winter the South African west coast is pounded by large waves arising from
south Atlantic storms. Large amounts of kelp are uprooted, and washed up onto the shore, where
it decomposes and is eaten by amphipods, isopods, and fly larvae.
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PERSONAL FOOD WEB WORKSHEET
1. Construct a simplified food web from the kelp tank using examples from each trophic level
as indicated below. Draw arrows connecting the categories, suggesting energy flow, and
the direction of energy flow. Note that these organisms are interdependent.
Primary producers
Herbivores
Secondary consumers
Suspension feeders
Decomposers
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2. Energy Flow through the kelp community. Compete the flowchart.
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5. RED ALGAE (DIVISION RHODOPHYTA)
The mid to lower intertidal of the Cape Peninsula is dominated to a large extent by red algae.
These form by far the largest group of sea plants on the Peninsula. Like the brown algae, many of
the reds are fleshy and bulky and generally occur lower down the shore because they are less
tolerant of salinity and temperature extremes when compared with some of the common green
sea plants. Below are the common red algae of the Cape Peninsula.
**Purple laver (Porphyra sp)
Porphyra species, commonly called purple laver, are extremely thin (only one cell
thick), flat, membranous plants. This sea plant looks like a sheet of wrinkled
cellophane when dry, crumpled and folded upon itself. They vary in colour from
yellow to purple to almost black. Species of Porphyra are abundant high up on the
shore where desiccation stress is at its greatest. While most sea plants are
intolerant of the conditions this high up the shore, Porphyra species are able to
survive here due to their remarkable recovery capabilities; this sea plant has been
shown to survive dehydration for over seven days. Purple laver is often collected to
use as the wrapping around sushi and can be dried, ground up and reformed to
make nori sheets, also used for sushi.
Tar crust (Hildenbrandia lecanellierii)
Another species tolerant of the desiccation stress high up on the shore, is
the encrusting red sea plant (Hildenbrandia lecanellierii). Looking
remarkably like splashed tar, this sea plant may form large expanses in the
upper intertidal, in crevices, and in places prone to sand inundation. Older
parts of the plant often become detached from the substrate, but it shows
a remarkable rate of recovery from physical disturbance and often may
regenerate from a few cells.
**Slippery orbits (Aeodes orbitosa)
Commonly known as slippery orbits this is another flat, slippery,
foliose sea plant that is also very tough. Its colour varies from yellowbrown to reddish-brown. This sea plant is especially common in the
mid- to lower intertidal zone where it often forms large expanses. In
sheltered intertidal pools, this sea plant has been known to grow to 2
meters in diameter.
**Tongue weed (Gigartina polycarpa)
This is a tough, fleshy sea plant bearing oval blades. Individuals of this species
are characteristically rough and bear numerous papillae (sometimes the
blades are even rippled) giving the appearance of a rough tongue. The colour
in this species varies from yellow-brown to reddish-brown to almost black.
Along with Aeodes it is also quite abundant in the mid- to lower intertidal
zone.
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**Hedgehog sea plant (Nothogenia erinacea)
Aptly called the hedgehog sea plant because of its appearance, this sea plant
consists of elongated foliaceous blades that are tough and leathery when wet,
becoming papery when dry. The blades bear numerous densely packed tuftlike outgrowths giving the sea plant its hedgehog-like appearance. This species
varies in colour from yellow-brown to almost black. It is also very common in
the mid to lower intertidal.
USES OF RED ALGAE (FLESHY)
While the algae industry in the Western world is based mainly on sea plant extracts, in the East
Sea plants are cultivated in huge volumes for human consumption. Much of this industry is based
on the red sea plants.
Of all the sea plants, the reds are probably the most valuable to humans economically.
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Purple laver (Porphyra) constitutes an astonishing 80% of all sea plant harvesting all over
the world. In Asia, purple laver is known as nori and is eaten as complete plant either dried
or in soups, or as tasty wrappings for sushi and rice. The iodine and high vitamin and protein
content of nori makes it attractive, as does the relative simplicity of its mariculture (sea
farming), which began more than 300 years ago in Japan.
Beside food for direct consumption, red sea plants are also important for their phycocolloid
extracts. Phycocolloids are sea plant derivatives that cause particles to remain suspended in
solution and are therefore excellent as stabilizing and gelling agents. The main phycocolloids
derived from red sea plants are carrageenan and agar.

Carrageenan is highly sought after in western societies where it is especially important in
the dairy industry. Milkshakes, cheese, yoghurts, powdered milk (including baby formula),
etc all possess red sea plant extracts. Believe it or not, carrageenan is even used in pet food,
cosmetics, shampoos, paints and toothpaste. A number of carrageenophyte sea plants are
being investigated in South Africa. These include green tips and various species of tongue
weed, twisted gigartina, and slippery orbits.
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Agar on the other hand, has its most important use as a medium on which to culture fungi
and bacteria in microbiological and medical pathology research. In food for human
consumption agar can be found in baking and confectionary products and is also widely
used to clarify wine, juice and vinegars due its excellent protein binding properties. In larger
industries, agar is used to make adhesives and capsules for tablets. South African
agarophytes include the sea plant genera Gracilaria (which is harvested extensively in
Saldanha Bay) and especially Gelidium.
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QUICK REVIEW
1. You are showing a visitor pieces of Purple Laver and Slippery orbit at the touch pool. How
do they differ, in terms of structure and feel? Will they be found in the same place on the
rocky shore?
2. What is the ‘most popular’ fact you should mention about Purple laver?
3. Name the two chemicals that can be extracted from fleshy red plants and some uses and
applications of each chemical.
4. After the children have felt the texture of some tongue weed, explain to the parents what
economically useful chemical(s) it contains, and some of their uses...
5.1 ENCRUSTING CORALLINE ALGAE
Beside the fleshy red sea plants mentioned above, there is another group of red sea plants that
are especially important in the formation of coral reefs,
an activity with which they have been intimately
involved in for millions of years. These reef-building red
sea plants are the encrusting coralline sea plants.
They are widespread in shallow water in all of the
world’s oceans, where they often cover close to 100 %
of rocky substrates and equally abundant throughout
the intertidal zone of the Cape Peninsula.
However, they are relatively unfamiliar, even to many
marine scientists. Encrusting coralline sea plants are
readily recognizable as pink, pinkish-grey, red, mauve
or purple blotches as though a clumsy painter’s apprentice spilled them all over the rock surfaces,
animals and even other sea plants.
Like all red sea plants, coralline algae possess the phycobilin photosynthetic pigments that give
them their red coloration. Unlike fleshy sea plants though, coralline algae are calcified (they have
their cell walls impregnated with lime) so that they are extremely hard.
These are some of the common encrusting coralline sea plants of the Cape Peninsula.
**Cochlear coralline (Spongites yendo)
Cochlear coralline is the most abundant encrusting coralline in the
intertidal, occurring from the mid intertidal to the immediate
subtidal. Its colour varies from grey-pink in well-lit areas, mauve in
shaded areas. Individuals of this species generally fuse together
when crusts meet so that large expanses of the coralline are often
thought of as a single sea plant. This coralline is closely associated
with the territorial gardening pear-shaped limpet, where it forms
an extensive covering of limpets’ shells and the base of limpet
zone. For this reason, this coralline is commonly known as the
cochlear coralline.
14
Two Oceans Aquarium Volunteer Training Manual – Module 3 - INTRO TO SEA PLANTS
Dinner plate coralline crust
(Heydrichia woelkerlingii)
Dinner plate coralline algae
abundant
encrusting
immediate subtidal. It is
mm), smooth, porcelainwith
individuals
easily
a dinner plate, therefore
coralline algae. It is also
coralline crust because of its smooth velvety nature.
or velvety coralline crust
are by far the most
coralline alga within the
extremely thick (up to 20
like encrusting coralline
attaining the diameter of
the name dinner plate
called
the
velvety
USES OF RED ALGAE (CALCIFIED)
Encrusting coralline sea plants too are important in the ecology of marine ecosystems where they
serve as food and shelter for many marine animals. Despite their hard, calcified nature, however,
they also have a number of economic uses.

They are used in medicine, and in more modern medical science coralline algae are used in
the preparation of dental bone implants.

Coralline rubble known as maerl is used in calcium mineral supplements, as soil pH
conditioners, in the filtration of acidic drinking water, and even as food additives for
livestock.

They are also used as “live rock” in the marine aquarium industry.

Coralline rock has even been used as building stones.
QUICK REVIEW
1. Mention 3 or 4 uses for calcified red algae.
Two Oceans Aquarium Volunteer Training Manual – Module 3 - INTRO TO SEA PLANTS
15
REPRODUCTION IN ALGAE (For interest)
The cycle of reproduction and growth to produce the next generation in organisms is referred to
as the life cycle of the organism. The life cycle of sea plants is varied and fascinating. Since they
are fixed to the substratum they depend on their spores for dispersal. Furthermore, as the chance
of the spores surviving is so slim they have to produce vast quantities. As an example, the sea
bamboo produces 10 000 spores per hour from each square centimetre of its fertile blades.
Life cycles involve two basic and simple processes: meiosis (cell division leading to the production
of spores) and syngamy (or fusion).


During meiosis, the number of chromosomes in a cell is halved.
During syngamy, the number of chromosomes is restored when two nuclei with half the
number of chromosomes are fuse together. The resulting nucleus has the full set of
chromosomes.
Reproduction in the sea plants common to the Cape Peninsula is generally of two kinds: gametic
and sporic life cycles.
1. GAMETIC LIFE CYCLES
In gametic life cycles, the product of
meiosis (where the number of
chromosomes is halved) is gametes.
This type of life cycle is common in
humans and most animals. Although
not as common in algae various species
of Codium have such a life cycle.
2. SPORIC LIFE CYCLES
Life cycle of the sea lettuce
16
In sporic life cycles, the product of
meiosis is spores. This is the life cycle
common to mosses for example. On
land the dominant free-living form that
one sees is called the sporophyte.
In sporic life cycles, spores produced
by the sporophyte give rise to freeliving male or female gametophytes
that in turn produce the gametes by
simple asexual reproduction.
Two Oceans Aquarium Volunteer Training Manual – Module 3 - INTRO TO SEA PLANTS
6. GLOSSARY
Algae
Blade (or Frond)
Algae are aquatic or live in damp habitats on land and include
unicellular organisms and multicellular green, red and brown sea
plants and freshwater algae such as Spirogyra.
Synonymous with leaves in green plants.
Dimorphic
Having two different forms.
Endemic
Occurring nowhere else in the world.
Epiphytic
Living on or attached to plants.
Foliose
Leaf-like in form or appearance.
Holdfast
The root-like organ of attachment.
Kelp
Giant brown sea plants that dominate the subtidal area.
Spring tide
Rhizomatous
That tide occurring every two weeks during new and full moon
phases. At this time, low tides are at their lowest, and high tides at
their highest.
A creeping stem-like structure.
Stipe
The flexible “stem” in sea plants.
Thallus
A plant body not differentiated into true leaves, stems and roots. It is
often a flattened structure.
An oceanographic process whereby cold nutrient rich subsurface
water moves to the surface to replace offshore moving surface
water. This phenomenon is especially prevalent on our west coast.
Upwelling
Based on an original document
Complied by Gavin W. Maneveldt
Botany Department, University of the Western Cape
Private Bag X17, Bellville 7535
7. REFERENCES
Sea Plant illustrations by M.L. Branch and R.H. Simons.
Life cycles, coralline sea plants and community illustrations by R. Frans.
Energy Flow illustration from the Pick ‘n Pay envirofacts sheet no 11.
Source of M.L. Branch and R.H. Simons illustrations:
Simons, R.H. 1976. Seaweeds of Southern Africa: Guide-lines for their study and identification. Fisheries
Bulletin of South Africa, 7: 1-113.
Branch, G. & M. Branch. 1981. The living shores of Southern Africa. Struik, Cape Town.
Two Oceans Aquarium Volunteer Training Manual – Module 3 - INTRO TO SEA PLANTS
17
SEA PLANTS MADE SIMPLE Recommended book: TWO OCEANS A guide to the marine life of Southern Africa. Branch G.M. et al. 1994: Sea plants pg 307-341 David Philip.
Notes and worksheet compiled by Philke Borgelt. Illustrations - fact sheets by Margo Branch
RED
Chlorophyll a + phycobilins (blue and red pigments)
absorb blue light.
BROWN
Chlorophyll a and c + fucoxanthin
(brown)
absorb blue-green light.
GREEN
Chlorophyll a and b + carotenoida
(yellow)
absorb violet and red light.
CATEGORY
SHAPE
COMMON NAME
Sea lettuce
(Ulva)
ZONE FOUND
Upper Balanoid
Sea intestine
Upper Balanoid
2OA EXHIBIT
Touch Pool
(Enteromorpha
intestinalis)
Upright codium
(Codium extricatum)
Sandy rock pools
Touch Pool
Strap caulerpa
(Caulerpa filiformis)
Sandy rocky pools
Dead-man's fingers
(Splachnidium rugosum)
Lower Balanoid
Intertidal
&
Seahorse
Touch Pool
Sea bamboo
(Ecklonia maxima)
Infratidal
Kelp Forest
Split-fan kelp
(Laminaria pallida)
Infratidal
(to depth of 30m)
Kelp Forest
Bladder kelp
(Macroccystis angustifolia)
Infratidal
(shallow)
Kelp Forest
Purple laver
(Porphyra capensis)
Littorina
Intertidal
Slippery orbit
(Aeodes orbitosa)
Lower Balanoid
Touch Pool
Tongue weed
(Gigartina radula)
Lower Balanoid
Touch Pool
Hedgehog sea plant
(Nothogenia erinacea)
Lower Balanoid
Touch Pool
Cochlear coralline
(Spongites yendoi)
Cochlear
Velvety coralline
crust(Heydrichia
woelkerlingii)
Infratidal
DESCRIPTION
Looks like green cellophane (wet).
Two cells thick, colonises easily.
Wide salt and temperature tolerance.
Tube one cell thick.
Colonises easily, opportunistic.
Wide salt and temperature changes.
Forked, velvety, spongy filaments. Lack
cross-walls
Chloroplasts moveable.
Annulated stipes diagnostic.
Flat blades with dark green spots.
Chloroplasts moveable.
Turgid (wet). Wrinkled (dry).
Filled with thick mucilage to withstand
desiccation.
Hollow stipe, float at apex.
Canopy of kelp forest dominant kelp of SW
coast.
Warty, mostly solid stipe.
Dominant kelp in NW coast
Rippled blade with gas filled bladder.
Found in sheltered water only at Kommetjie
and Robben Island.
Slippery (wet);
Like crumpled plastic bag (dry).
Yellow margin ; pink margin .
Water loss from mucilage, not cells.
Yellowish or olive-brown.
Tough and very slippery.
Unpalatable to grazers.
Yellow-brown to red-brown.
Tough, gametophyte - many papillae
tetrasporophyte -ridges and grooves.
Yellow-brown to black.
Tuft -like outgrowths more in gametophyte
than tetrasporophyte.
Chalky - white, lime laden, knobbled.
Associated with territorial gardening pearshaped limpet.
Deep purple-pink, glossy velvet to touch.
Abundant porcelain-like "dinner plate".
USES TO MAN
Food especially in Far East in salads, soups.
Beta-carotene as a yellow-orange colorant in cheese, margarine,
mayonnaise etc.
Kelp (means 'ash') used as fertiliser.
Root hormone  increase crop yield
Food for abalone farming.
Iodine. Powdered kelp exported to Japan for fish feed.
Kelp exported for extraction of alginate
Kelp sludge and seeds to prevent erosion.
Alginic acid fixes radioactive strontium.
Natural population too small to warrant harvesting.
Called 'nori': in Far East.
Used for sushi, soups, crushed in savoury biscuits.
Mariculture in Japan began in 18th century.
Carrageenan – binding properties used in toothpaste, paints, baby formula,
ice-cream, beer foam.
At Saldana Bay
Beach-cast Gracilaria collected, dried and exported for agar extraction.
In Eastern Cape, Gelidium jelly weed is harvested for export.
Used in confectionery, culture medium, clarifying wine.
Dentures:
Maerl (coralline rubble) in calcium. Mineral supplements food additive for
livestock.
Filtration of acidic drinking water.
Soil pH conditioners.